feat: Rust std target + ruststd tests; SYS_EXIT_GROUP; fix mkdir/create under missing parent

kernel/src/Api/Filesystem.hpp

@@ -27,6 +27,23 @@ namespace montauk::abi {
         return required == 0 || Sched::HasCapability(required);
     }
 
+    // Drivers fail a create under a missing parent with a bare -1; report it
+    // as NoSuchPath so callers can tell it apart (Rust's create_dir_all only
+    // creates the missing ancestors when mkdir says NotFound).
+    static bool ParentDirExists(const char* resolved) {
+        char parent[256];
+        int len = Lib::strlen(resolved);
+        if (len >= (int)sizeof(parent)) return false;
+        memcpy(parent, resolved, len + 1);
+        while (len > 0 && parent[len - 1] == '/') len--;
+        while (len > 0 && parent[len - 1] != '/') len--;
+        while (len > 0 && parent[len - 1] == '/') len--;
+        if (len == 0 || parent[len - 1] == ':') return true;  // drive root
+        parent[len] = '\0';
+        Fs::Vfs::StatInfo info;
+        return Fs::Vfs::VfsStat(parent, info) == 0 && info.isDir;
+    }
+
     static int Sys_Open(const char* path) {
         char resolved[256];
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return InvalidArgument;
@@ -117,6 +134,7 @@ namespace montauk::abi {
         char resolved[256];
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return InvalidArgument;
         if (!CanModifyFilePath(resolved)) return SystemIntegrityError;
+        if (!ParentDirExists(resolved)) return NoSuchPath;
         return Ipc::CreateFileHandle(resolved);
     }
 
@@ -171,6 +189,7 @@ namespace montauk::abi {
         char resolved[256];
         if (!ResolveProcessPath(path, resolved, sizeof(resolved))) return InvalidArgument;
         if (!CanModifyFilePath(resolved)) return SystemIntegrityError;
+        if (!ParentDirExists(resolved)) return NoSuchPath;
         return Fs::Vfs::VfsMkdir(resolved);
     }